In electrophotographic printing devices, toner particles are used to form the desired image on the print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure.
A variety of different techniques have been developed to heat the fusing roller. One of the most common techniques for heating a fusing roller uses a quartz lamp placed inside the roller. The lamp is turned on to heat the fusing roller during printing. In this configuration, the roller is typically made of a central core of a material having a high level of heat conductivity such as aluminum or similar metal or alloy. The central core may be covered by an elastic or rubber coating to facilitate fusing of the plastic ink media (i.e., toner) onto a paper or other web-like printing substrate. One example of the state of the art in this field is U.S. Pat. No. 6,236,830 (the “'830 patent”) issued May 22, 2001 to Hoberock, et al. describes a heated fuser roller including a series of heating wires embedded within the roller. The '830 patent is expressly incorporated by reference herein in its entirety.
Heat generated by the lamp must heat the entirety of the roller prior to operation of the device. Since the roller constitutes a significant thermal mass, it requires substantial time and energy to raise the temperature of the roller to an acceptable operating range.
So called “instant-on” fusers were developed to reduce warm-up time, eliminate the need for standby power and improve print quality in single page or small print jobs. U.S. Pat. Nos. 5,659,867 (the “'867 patent”), 5,087,946 (the “'946 patent”), and 4,724,303 (the “'303 patent”) describe instant-on type fuser heaters that utilize a thin walled heated fusing roller. In the '867 patent, the heating element is a group of resistive conductors positioned on the surface of a thin walled ceramic tube. The conductors are overlaid with a glassy coating to provide a smooth exterior surface for the ceramic tube. In the '946 patent, the heating element is a conductive fiber filler material added to the plastic composition that forms the wall of the roller. In the '303 patent, the heating element is a resistance heating foil or printed circuit glued to the inside surface of the thin metal wall of the roller.
While these “instant-on” fusers having embedded heating elements may be advantageous because the heating element is near the surface of the roller, substantial changes must be made to conventional fuser roller designs to incorporate both techniques. Hence, these techniques cannot be easily incorporated into the more common fuser roller designs. Further, in contrast, conventional internal heating of a fuser roller takes substantial warm-up time and associated energy requirements.